Well I haven't sold the preamp yet, but I finally found the right combination to have it all working !
Paul's help had me understand part of what a ground loop is made of. Reading a little more helped me to get a little deeper into it.
As I understand it, in gross the principle is as follow: 2 components that are not interconnected in any way should be connected to Earth when there is a mean for it (a 3 prong connection).
As soon as you connect 2 components together (interconnect that ties them together), a "triangle" can appear. It is not always bad, but it can trigger a ground loop. When this occurs, to correct this, all that is need is to remove the connection to Earth for one of the 2 components, since ground will travel between the 2 components and exit through the component still connected to Earth.
It is not automatically how it turns. Having 2 components connected together, with each of them on a different AC circuit still follows the same rules, as it normally lands on the same rail in the main electrical panel. Well that would be like this here in Canada.
But don't ask me more ! There are lots of other situations (hadware grounding inside a component), between themselves, etc... I already have forgot the path a few billion electrons have chosen to follow since I did all these attempts...
So, logically, as I understood it, if I have a PC, DAC, preamp, power amp, all connected together, BECAUSE I HAD A NOISE, this meant that I should only have one of these 5 components connected to Earth. Easy...
Not so !
That was my starting idea. Like I said, this is a gross view of a situation where there could be a ground loop.
So with this in mind, I only connected the PC to Earth and lifted all the rest.
But I forget to descrie the noise I wanted to get rid of. It was not a "hum" as we generally think of when someone says "ground loop alert !". No, it was a thin sound, some kind of frequency that maybe someone has heard when an electronic chip starts "singing" depending on the amount of current going through it. Or you could compare this to a light bulb emitting a sound when you play with a dimmer...
So, I was not sure if I was going for a ground loop or for a defective piece of hardware... Lucky me...
It took me a long time to discover how to get rid of it. Today, finally, with the help of an old integrated amplifier I have here since 1984 (NAD 3020B), I finally stopped hearing that noise. This old but faithful little amp as a 2 prong connection ?
So now I have this configuration:
- PC - to Earth
- USB cable (nothing special about it)
- NOS1 dac -
Not connected to Earth (2013/09/17)
- RCA interconnects
- Preamp -
Not connected to Earth (2013/09/17)
- RCA interconnects
- Power amp - Not connected to Earth
All of this is on the same AC outlet by the way ! I will eventually separate them, but at this time the need to simplify things had me doing things like this.
I know that Peter suggested to me to have the Earth lifted for the NOS1. I tried it but to no avail. What worked for someone will not necessarily work for someone else.
What are the conclusions today ? I don't know. I would not be honest to say that I understand all of it. It was a matter of "trial and error"...
For those who will eventually encounter this situation: if you have old speakers you don't mind to damage, please use them instead ! I almost blew my speakers while doing something that I thought was not dangerous.
It can help to have a few spare components. I have 3 amps here, so I was able to eliminate some components I was questionning out of the equation.
Playing with protective earth is not a subject to take lightly. It can be dangerous - for you and your equipment.
Alain